Method and apparatus for sheathing cable cores

ABSTRACT

A method and apparatus for sheathing a cable core with a strip of sheathing material are described wherein the strip is crimped with crimping means to give it inherent longitudinal stretchability, stretched to the point where the crimp is substantially removed so that the longitudinal edges of the strip are of substantially equal effective length; and wrapped about the cable core to form a sheath in which the longitudinal edges of the strip overlap. The method and apparatus seeks to overcome the problems of buckling that arise with sheathing material wherein the longitudinal edges of the material are of different length.

United States Patent Beach Aug. 19, 1975 [54] METHOD AND APPARATUS FOR 3,144,974 8/1964 Eichner et al. 1 13/120 G SHEATHING CABLE CORES 3,397,442 8/1968 McGean 3,503,112 3/1970 Siegel [75] Inventor: Shirley M. Beach, North Vancouver, 3,7 9, 97 11 1973 Priaroggia et al,, Canada 3,772,772 11/1973 Lehnert 3,779,846 12 1973 K1 k 156 144 73 Assignee: Phillips Cables Limited, Brockville, ey amp Canada Primary Examiner-C. W. Lanham [22] Filed: July 2, 1973 Assistant ExaminerJames R. Duzan Attorney, Agent, or FirmDiller, Brown, Ramik & [2]] Appl. No.. 375,646 Wight [30] Foreign Application Priority Data ABSTRACT Jul 6, 1972 Canada 146559 A method and apparatus for sheathing a cable core with a strip of sheathing material are described [52] US. Cl. 29/458; 29/509; 72/187; wherein the strip is crimped with Crimping means to 72/385 give it inherent longitudinal stretchability, stretched to [51] Int. Cl B23 3/00 th p in where the crimp is substantially removed so [58] Fi ld of Sear h 29/458, 460, 505, 202, 5 that the longitudinal edges of the strip are of substan- 29/600, 477.3; 156/143; 72/385, 48, 49, 50, tially equal effective length; and wrapped about the 168 187, 196; 93/77, 80, 79, 94 R, 94 M cable core to form a sheath in which the longitudinal edges of the strip overlap. The method and apparatus [56] Referen Cited seeks to overcome the problems of buckling that arise UNITED STATES PATENTS with sheathing material wherein the longitudinal edges 2,991,550 7/1961 Block 29/460 of the matera] are of dfferem length 2,998,339 8/1961 Barnes et al. 29/460 12 Claims, 1 Drawing Figure METHOD AND APPARATUS FOR SHEATHING CABLE CORES BACKGROUND OF THE INVENTION This invention relates to a method and apparatus for sheathing cable cores and more particularly to a method and apparatus in which a sheath is wrapped longitudinally about a cable core.

In the formation of certain types of cable, strips of sheathing material are wrapped longitudinally about a cable core as the core is advanced longitudinally to form a cylindrical sheath with overlapping longitudinal edges. A seam is formed at the overlapping edges to retain the strip around the cable core.

The production of a strip or tape with edges of equal length is difficult and in practice one edge is often slightly longer than the other. This difference can be observed by viewing a long length of strip or tape longitudinally, otherwise the difference is usually so slight as to be almost unnoticeable.

When a strip of such sheathing material is applied longitudinally to a cable core, the longer edge tends to buckle at various points along its length producing a sheath having an irregular surface.

The buckles in the sheath introduce an unevenness into a jacketing material which is subsequently applied over the sheath and which can result in a flaw or defect in the cable.

The sheath may, for example, comprise a metallic tape which may be coated on one or both sides with a thermoplastic material, for example, polyethylene and in this case the invention also provides an improved means for sealing the overlap of the sheath material to provide a secure covering around the cable core in which the cable core with the sheath material wrapped around it is drawn through a heated tube at a temperature sufficient to soften or melt the thermoplastic material, and form a bond between the overlapping edges of the sheath material.

In the case in which a jacket of protective material is to be extruded around the sheathed cable core, the tube will preferably draw its heat from the extruder head. This heat may be supplemented by other heating or cooling means depending on the temperature necessary to produce the bond.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of sheathing a cable core.

It is a further object of the present invention to provide apparatus for sheathing a cable core.

In accordance with the present invention a method of sheathing a cable core advanced longitudinally, with a strip of sheathing material, comprises crimping the strip to give it inherent longitudinal stretchability, stretching the crimped strip longitudinally to the point where the crimp is removed to substantially the maximum where the longitudinal edges of the strip are of substantially equal effective length and wrapping the strip longitudinally about the cable core to form a sheath in which the longitudinal edges of the strip overlap.

In one feature of the invention the sheathing material has a coating of a thermoplastic material on at least one side and the cable core with the sheath wrapped around it is passed through a heated tube whereby the heat from the tube softens the thermoplastic material and the overlapping edges of the sheath arebonded together. The tube may be disposed between the sheath wrapping means and an extruder head adapted to extrude a jacket of protective material around the sheathed cable core, the tube drawing its heat from the extruder head.

In accordance with another aspect of the present invention, apparatus for sheathing a cable core advanced longitudinally with a strip of sheathing material comprises means for crimping said strip to give it inherent longitudinal stretchability, means for stretching the crimped strip longitudinally to the point where the crimp is removed to substantially a maximum where the longitudinal edges of the strip are of substantially equal effective length and sheath forming means for wrapping the strip longitudinally about the cable core to form a sheath in which the longitudinal edges of the sheath overlap.

In one feature of this aspect of the invention, the apparatus may include a tube through which the sheathed cable core can be passed, so constructed and arranged that heat delivered to the tube is transferred to said sheath. The tube may be attached to an extruder head of an extrusion apparatus adapted to extrude a jacket of protective material around a sheathed cable core, the tube drawing its heat from the extruder head.

The term crimping includes any type of like controlled deformation which has the effect of shortening the length of the strip while it remains deformed, but which is substantially but not entirely removed by stretching the strip close to its normal undeformed length so that when it is so stretched its opposite edges will have, to all intents and purposes, the same effective length. This enables the strip to be applied to the cable without the resulting buckling at one edge of the strip, as occurs with a strip to which controlled deformation has not been applied.

Although the preferred form of crimping consists of a series of corrugations, each extending across the whole width of the strip of sheathing material, other forms may be used for example, spaced indentations of transverse width less than that of the strip so distributed that the strip is rendered extensible across its whole width by longitudinal stretching which removes or reduces the indentations.

Examples of crimping are controlled creasing, wrinkling or rumpling, and creping. The deformation may also comprise embossements or indentations and the like preferably arranged in rows extending transversely of the strip from the edges.

BRIEF DESCRIPTION OF THE DRAWING A preferred embodiment of the invention is illustrated with reference to the accompanying drawings in which there is illustrated schematically the method and apparatus according to the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS With reference to the drawing, an aluminium strip or tape 1 of sheathing material coated on both sides with polyethylene is fed from a roll 2 between a pair of driven corrugating rolls 3, which are adjusted to impart a slight corrugation transversely of the strip 1. The corrugating rolls 3 are driven by a variable speed motor 4.

The strip 1 passes from corrugating rolls 3 around a smooth guide roll 5, a smooth dancer roll 6 and a smooth guide roll 7.

Smooth dancer roll 6 is connected to a movable dancer arm 8 from which is suspended a weight 9 which controls the tension in strip 1. The dancer arm 8 is pivoted about a pivot 10 and operatively connected to a control device, for example, a rheostat (not shown), for controlling the variable speed motor 4.

The strip 1 after passing over smooth guide roll 7 passes through a sheath former 12 which wraps the strip 1 longitudinally around a cable core 1 1 so that the longitudinal edges overlap. The sheathed core 13 passes from the sheath former 12 through a heated steel tube 14 attached to the extruder head 15 of an extrusion apparatus 16, where a seal is formed in the overlapping edges of the strip 1, and into the extruder head 15 of extrusion apparatus 16 where a jacket of protective material for example polyethylene is extruded around the sheathed core 13.

In operation the corrugating rolls 3 may be adjusted by the operator to introduce a slightly deeper corrugation in the longitudinal edge of strip 1 which is of greater length. The edge of greater length is readily apparent when 10 or 15 feet of the strip 1 is inspected. The longer edge may be, for example, curved or it may be straight but in a non-parallel relationship with the other edge.

Dancer roll 6 rises and falls with variation of the tension in the strip 1, the movement of dancer roll 6 actuates movable dancer arm 8. When the dancer arm 8 rises, the control device at the pivot 10 increases the speed of the variable motor 4 and when the dancer arm 8 falls the control device decreases the speed of variable motor 4. This variation ensures the retention of sufficient tension in the strip 1 to remove substantially all of the corrugations from the strip 1 and the corrugations are removed as the strip 1 emerges from between the corrugating rolls 3.

The sheath former 12 may be, for example, a belt former or a simple series of rollers or guides adapted to wrap the strip 1 longitudinally around the cable core 11. One such apparatus for sheathing cable cores is shown in Canadian Pat. No. 725,969 Helmut E. Durr, issued Jan. 18, 1966.

It will be appreciated that the amount of crimping or deformation can be varied over a wide range. At the lower end of the range it should be sufficient to accomodate the difference in length between the two longitudinal edges of the strip 1. There is no real upper limit to the amount of crimping or deformation which may be introduced; clearly, if a large amount of crimping is introduced then the weight 9 should be adjusted accordingly, to remove the crimping. A suitable range for most purposes would be of the order of l to 10 percent.

In general an amount of crimping or deformation in strip 1 of the order of about 5 percent is found to be satisfactory, for example, when the strip 1 is deformed out of its normal plane by the introduction of corrugations a strip 1,000 ft. in length is reduced in effective length by 50 ft. due to the folds.

In the preferred form of crimping, corrugations are applied transversely of the strip 1, there being approximately 10 corrugations per inch, each corrugation having a depth of 3 to 5 thousandths of an inch.

The number of corrugations may however be varied over a wide range, the number being dictated by similar considerations as for the amount of cimpring. By way of example, a suitable range for the number of corrugations per inch would be 5 to 20 corrugations per inch.

The strip 1 is suitably a metallic strip, for example, of aluminium, copper or brass having a width sufficient to surround the cable core 11 and provide an overlap at the edges of about 0.125 to 0.25 inches and a thickness of about 0.008 inches, particularly when the cable is a telephone cable and the sheath is to act as a shield to protect the cable conductors of the cable core 11 against external electrical signals and to act as a barrier to the penetration of moisture. The barrier properties of such a shield are improved by a coating of a waterproof material, for example, a polyethylene preferably on both sides of the shield, and this coating provides means for forming a bond between the overlapping edges of the sheath in heated tube 14.

In the method described above corrugations are formed in a strip 1. It will be apparent however that the crimping could be introduced during the manufacture of the strip 1.

Instead of corrugating rolls 3, respective rolls having a surface embossed with small indentations and projections could be employed to emboss the strip 1 and thus render it extensible.

I claim:

1. A method of sheathing a cable core advanced longitudinally, with a flat strip of sheathing material, comprising:

advancing said strip and advancing said cable core,

crimping said strip to give it inherent longitudinal stretchability, the crimps extending inwardly from the longitudinal edges of the strip, stretching the crimped strip longitudinally to the point where the crimp is removed to substantially the maximum where the longitudinal edges of the strip are of substantially equal effective length and wrapping the strip longitudinally about the cable core to form a sheath in which the longitudinal edges of the strip overlap.

2. A method according to claim 1 wherein said crimping comprises passing the strip between corrugating rolls which introduce corrugations transversely of the strip.

3. A method according to claim 2 wherein the corrugations are such that the strip is reduced in length by the order of l to 10 percent of its normal length.

4. A method according to claim 3 wherein the strip is corrugated to the extent of about 5 to 20 corrugations per inch, each corrugation being 3 to 5 thousandths of an inch deep.

5. A method according to claim 1 wherein the sheathing material has a coating of a thermoplastic on at least one side and said cable core with said sheath wrapped around it is passed through a heated tube whereby the heat from the tube softens the thermoplastic material and the overlapping edges of the sheath are bonded together.

6. A method according to claim 5 wherein said tube is disposed adjacent an extruder head adapted to extrude a jacket of protective material around the sheathed cable core, the tube drawing its heat fromthe extruder head.

7. A method according to claim 6 wherein the strip is a metallic strip coated with polyethylene.

8. Apparatus for sheathing a cable core advanced longitudinally with a flat strip of sheathing material comprising, means for advancing a cable core and means for advancing a strip of sheathing material,

means for crimping said strip to give it inherent longitudinal stretchability, with crimps extending inwardly from the longitudinal edges of the strip, means for stretching the strip longitudinally to the point where the crimp is removed to substantially a maximum where the longitudinal edges of the strip are of substantially equal effective length, and sheath forming means for wrapping the strip longitudinally about the cable core to form a sheath in which the longitudinal edges of the sheath overlap.

9. Apparatus according to claim 8 further including a tube through which the sheathed cable core can be passed, so constructed and arranged that heat delivered varying in depth transversely of the strip. 

1. A method of sheathing a cable core advanced longitudinally, with a flat strip of sheathing material, comprising: advancing said strip and advancing said cable core, crimping said strip to give it inherent longitudinal stretchability, the crimps extending inwardly from the longitudinal edges of the strip, stretching the crimped strip longitudinally to the point where the crimp is removed to substantially the maximum where the longitudinal edges of the strip are of substantially equal effective length and wrapping the strip longitudinally about the cable core to form a sheath in which the longitudinal edges of the strip overlap.
 2. A method according to claim 1 wherein said crimping comprises passing the strip between corrugating rolls which introduce corrugations transversely of the strip.
 3. A method according to claim 2 wherein the corrugations are such that the strip is reduced in length by the order of 1 to 10 percent of its normal length.
 4. A method according to claim 3 wherein the strip is corrugated to the extent of about 5 to 20 corrugations per inch, each corrugation being 3 to 5 thousandths of an inch deep.
 5. A method according to claim 1 wherein the sheathing material has a coating of a thermoplastic on at least one side and said cable core with said sheath wrapped around it is passed through a heated tube whereby the heat from the tube softens the thermoplastic material and the overlapping edges of the sheath are bonded together.
 6. A method according to claim 5 wherein said tube is disposed adjacent an extruder head adapted to extrude a jacket of protective material around the sheathed cable core, the tube drawing its heat from the extruder head.
 7. A method according to claim 6 wherein the strip is a metallic strip coated with polyethylene.
 8. Apparatus for sheathing a cable core advanced longitudinally with a flat strip of sheathing material comprising, means for advancing a cable core and means for advancing a strip of sheathing material, means for crimping said strip to give it inherent longitudinal stretchability, with crimps extending inwardly from the longitudinal edges of the strip, means for stretching the strip longitudinally to the point where the crimp is removed to substantially a maximum where the longitudinal edges of the strip are of substantially equal effective length, and sheath forming means for wrapping the strip longitudinally about the cable core to form a sheath in which the longitudinal edges of the sheath overlap.
 9. Apparatus according to claim 8 further including a tube through which the sheathed cable core can be passed, so constructed and arranged that heat delivered to said tube is transferred to said sheath.
 10. Apparatus according to claim 9 in which the tube is attached to an extruder head of an extrusion apparatus adapted to extrude a jacket of protective material around a sheathed cable, said tube drawing its heat from the extruder head.
 11. Apparatus according to claim 8 in which the means for crimping comprise corrugating rolls.
 12. Apparatus according to claim 11 wherein the corrugating rolls are adjustable to introduce corrugations varying in depth transversely of the strip. 